1. Field of the Invention
The present invention relates to an image displaying projector for projecting an image onto a screen and a light tunnel structure in an image displaying projector.
2. Description of the Related Art
An image displaying projector is known for producing an optical image on its imaging device from its image data supplied by a personal computer or a video camera and projecting it on a screen for display. Such a conventional image displaying projector includes commonly an image projection system shown in FIG. 9 where a light tunnel 92 is provided for condensing and collimating the light received from a lamp 90. In the image projection system, the light emitted from the lamp 90 (its optical axis denoted by the one-dot chain line with the arrow) is colored by a color wheel 91 and then condensed and collimated by the light tunnel 92 before compensated for waveform effects by a corrective lens 93. The light from the lamp 90 is reflected by a mirror 94, converged by a relay lens 95, and directed to an imaging device 96. As the light is reflected on an image forming plane of the imaging device 96, an image produced on the image forming plane can be projected by a projection lens 97.
Those components in the conventional image displaying projector are commonly assembled together with a support base 98 and installed in a housing, as shown in FIG. 10. Meanwhile, the color wheel 91 is not illustrated for simplicity. The lamp 90 is separately provided as it has to be replaced with a new one. The light tunnel 92 comprises four glass members bonded together to a tubular shape and mounted to the support base 98 by a metal retainer spring (fitting) 99 pressing down. The retainer spring 99 has a set of elastic press-down tabs 99e, 99f, 99g, and 99h as best shown in FIG. 11. When the retainer spring 99 is joined by screws (not shown) to the support base 98, its press-down tabs 9e, 99f, 99g, and 99h securely hold down the light tunnel 92.
It is however necessary for the light from the lamp 90 effectively reflecting on the imaging device 96 to adjust the angle at which the light tunnel 92 is mounted to the support base 98. The angle adjustment for the light tunnel 92 is conducted with an angle adjusting spring (not shown) operated to lift up and hold the light tunnel 92 and then pressed down by a couple of angle adjusting screws (not shown).
The corrective lens 93 has two lenses 93a and 93b held together to the inner wall of a metal tube 93e by retainer rings 93c and 93d respectively, as shown in FIG. 12. The corrective lens 93 of an assembly is mounted to the support base 98 at the output end of the light tunnel 92, as shown in FIG. 13.
Alternatively in a projection display using a space light modulator such as a liquid crystal light valve, a light tunnel arranged in the cross section to match a geometrical shape of the space light modulator is provided between the light source lamp and the space light modulator for optimizing the intensity of light to be projected onto a screen (for example, as disclosed in Japanese Patent Laid-Open Publication HEI8-271854). Also, a liquid crystal projector is introduced in which a light tunnel arranged to match in the aspect ratio with an imaging device is provided between the light source and the imaging device (for example as disclosed in Japanese Patent Laid-Open Publication HEI8-286146). Moreover, an illuminating apparatus for a projector is equipped with a light tunnel of which the input end for receiving light from the light source is smaller in the cross section than the output end (for example, as disclosed in Japanese Patent Laid-Open Publication HEI10-48476).
The light tunnel in the conventional image displaying projector however has the four glass members bonded by an adhesive to a tubular form thus increasing the steps of production and resulting in the cost up. Also, the light tunnel of the glass members is mounted to the support base by the retainer spring of an extra component. Furthermore, as the light tunnel is exposed to the light from the lamp, it is heated up and its glass members which are low in the radiation of heat may deteriorate or fracture. When the light emitted from the lamp is incident to one end plane of the light tunnel, it enters the glass members and its output from the other end may interrupt the image to be projected.
The adjustment of the angle for the light tunnel is made by the angle adjusting spring lifting the light tunnel and the angle adjusting screws determining the angle. Accordingly, its arrangement becomes intricate while the action of the angle adjusting is not easy. The corrective lens has the two lenses held in the lens holding tube with retaining rings and the assembly is mounted to the support base. This will increase the number of the components as well as the number of the production steps and hardly reduce the cost. Also, the other prior arts disclosed in Japanese Patent Laid-Open Publications HEI8-271854, HEI8-286146, and HEI10-48476 fail to eliminate the foregoing drawbacks.